Methods for controlling lithographic apparatus, lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic apparatus applies a device pattern at multiple fields across a substrate. A height map is decomposed into a plurality of components. A first height map component represents topographical variations associated with the device pattern. One or more further height map components represent other topographical variations. Using each height map component, control set-points are calculated according to a control algorithm specific to each component. The control set-points calculated for the different height map components are then combined and used to control imaging of the device pattern to the substrate. The specific control algorithms can be different from one another, and may have differing degrees of nonlinearity. The combining of the different set-points can be linear. Focus control in the presence of device-specific topography and other local variations can be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase entry of PCT patentapplication no. PCT/EP2016/065834, which was filed on Jul. 5, 2016,which claims priority of European patent application no. 15177572.3,which was filed on Jul. 20, 2015, and which is incorporated herein inits entirety by reference.

BACKGROUND Field of the Invention

The present disclosure relates to lithographic apparatus. The disclosurerelates in particular to the control of lithographic apparatus usingheight maps. The disclosure further relates to methods of manufacturingdevices by lithography, and to data processing apparatuses and computerprogram products for implementing parts of such apparatus and methods.

Background Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,comprising part of, one, or several dies) on a substrate (e.g., asilicon wafer). Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a grid ofadjacent target portions referred to as “fields” that are successivelypatterned. Known lithographic apparatus include so-called steppers, inwhich each field is irradiated by exposing an entire field pattern ontothe field at one time, and so-called scanners, in which each field isirradiated by scanning the field pattern through a radiation beam in agiven direction (the “scanning”-direction) while synchronously scanningthe substrate parallel or anti-parallel to this direction.

The pattern is imaged onto the target portion of the substrate usinglenses (or mirrors) forming a projection system. When imaging thepattern onto the substrate it is desirable to ensure that an uppermostsurface of the substrate (i.e. the surface onto which the pattern is tobe imaged) lies within the focal plane of the projection system.

The surface of a substrate on which a pattern should be projected isnever perfectly flat, but presents many height deviations on both alarge scale and smaller scale. Failure to adjust the focus of theprojection system may result in poor patterning performance andconsequently poor performance of the manufacturing process as a whole.Performance parameters such as critical dimension (CD) and CD uniformityin particular will be degraded by poor focus.

To measure these height deviations, height sensors are normallyintegrated in the lithographic apparatus. These are typically opticalsensors used to measure and the vertical position of the uppermostsurface of the substrate at points all across the substrate, after ithas been loaded into the lithographic apparatus. This set ofmeasurements is stored in some suitable form and may be referred to as a“height map”. The height map is then used when controlling imaging ofthe pattern onto the substrate, to ensure that the radiation sensitiveresist layer on each portion of the substrate lies in the focal plane ofthe projection lens. Typically the height of a substrate support bearingthe substrate will be adjusted continuously during exposure ofsuccessive portions on a substrate. Examples of height sensors aredisclosed in U.S. Pat. No. 7,265,364 B2, US 20100233600 A1 and US2013128247 A. They do not need to be described in detail herein.Corrections to the height map may be made using other sensormeasurements (for example an air gauge) to reduce process dependency ofthe measurements. According to patent application EP14157664.5, notpublished at the present priority date, further corrections can beapplied to the height map based on prior knowledge of product design andprocess dependency.

A number of problems may arise when controlling focus of the projectionsystem using height map data. In a scanning mode of lithography, aslit-shaped “aerial image” is formed and scanned over a field area toapply the field pattern. Height and tilt parameters of the aerial imageare adjusted dynamically to optimize focus performance throughout thescan. A known problem in lithography is that the substrate and/or thesubstrate support may exhibit local topographical variations that arechallenging for the focus controller. Such local variations may be, forexample, a bump due to contamination beneath the substrate. Another typeof local variation is a dip (hole) due to a gap in the “burls” thatsupport the substrate. Other local variations are associated with thesubstrate edge. The term “edge roll-off” has been coined to refer tosome types of edge topography phenomenon. Any non-device specifictopography related to the edge region of the substrate, as well as localvariations at any region of the substrate, should be considered asrelevant for the present disclosure.

The normal control algorithms of the imaging operation may be unable toachieve the best focus across such local variations. For such cases,differently weighted algorithms may be considered. On the other hand,there are also occasions when local variations are to be de-weighted, iffocus performance and yield are to be optimized. An example of such asituation is when the substrate is subject to device-specifictopographical variations. Some designs and processes yield a pattern oftopographical variations due to different processes and materials usedat different parts of the device. Modern device types such as 3-D NANDmemory devices are an example. Even where there is not a great actualtopographic variation, differences in optical properties of materialscan lead to a large apparent topographical variation, when read by theheight sensor. In cases with such significant device-specifictopography, it is generally desired for the focus control algorithm tobe insensitive to the local variations. This can be true not only forapparent variations caused by process dependency of the height sensor,but also for real topography variations. This is because trying tofollow short-range (high spatial frequency) variations generally worsensthe dynamic performance of the imaging system. Therefore, even if thisinsensitivity leads to defocus as topography is less accuratelyfollowed, it may still yield a net focus gain.

Unfortunately the same types of device that exhibit extremedevice-specific topography may also be particularly susceptible tobumps, holes and edge effects in the substrate. In any case, there areincreasingly conflicting requirements for the operator seeking tooptimize focus control for some modern semiconductor products. Theoperator struggles to achieve an optimum focus control algorithm. To alarge extent, in these cases there simply is no optimum algorithm, amongthose available.

SUMMARY OF THE INVENTION

It is desirable to improve performance of lithographic manufacturingprocesses in the presence of both device-specific topography andlocalized effects such as bumps and holes. It is a particular aim of thepresent disclosure to address the problem of focus control when imagingpatterns on such substrates. It is another aim of the disclosure toenable simpler operation of lithographic apparatus, and in particular tosimplify the selection of an optimized focus control algorithm.

The invention in a first aspect provides a method of controlling alithographic apparatus to manufacture a plurality of devices on asubstrate, the method comprising:

(a) obtaining a height map representing a topographical variation acrossthe substrate; and

(b) using the height map to control a positioning system of thelithographic apparatus for applying a device pattern at multiplelocations across the substrate

wherein step (b) comprises:

(b1) decomposing the height map into a plurality of components,including a first height map component representing topographicalvariations associated with the device pattern and one or more furtherheight map components representing other topographical variations;

(b2) using each height map component, calculating control set-pointsaccording to a control algorithm specific to each component; and

(b3) combining the control set-points calculated for the first heightmap component and the further height map component(s) and using thecombined set-points to control the positioning system to apply thedevice pattern to the substrate.

The invention in a second aspect provides an apparatus for controlling apositioning system of a lithographic apparatus for applying a devicepattern at multiple locations across a substrate, the apparatuscomprising a data processing apparatus programmed to perform the stepsof:

-   -   receiving a height map of a substrate that has been subjected to        lithographic processing over a plurality of device areas;    -   decomposing the height map into a plurality of components,        including a first height map component representing        topographical variations associated with the device pattern and        one or more further height map components representing other        topographical variations;    -   using each height map component, calculating control set-points        according to a control algorithm specific to each component; and    -   combining the control set-points calculated for the first height        map component and the further height map component(s) and    -   providing set-points to control the positioning system to apply        the device pattern to the substrate.

In accordance with the above aspects of the present disclosure, a focuscontrol method can be implemented that has different responsecharacteristics to device-specific topography compared with othertopography (such as holes or focus spots). In particular embodiments, afirst control algorithm applied to the device-specific component can bedesigned not to apply a great weight to extreme height values, while asecond control algorithm applied to the other topographical variationscan apply a greater weight to extreme values.

In an extreme example, the focus control may be performed without usingthe device specific component to calculate control set-points at all.Accordingly, the invention in a third aspect provides a method ofcontrolling a lithographic apparatus to manufacture a plurality ofdevices on a substrate, the method comprising:

(a) obtaining a height map representing a topographical variation acrossthe substrate; and

(b) using the height map to control a positioning system of thelithographic apparatus for applying a device pattern at multiplelocations across the substrate

wherein step (b) comprises:

(b1) subtracting from the height map a first height map componentrepresenting topographical variations associated with the device patternso as to obtain one or more further height map components representingother topographical variations;

(b2) using the obtained height map component(s), calculating controlset-points according to a control algorithm specific to the othertopographical variations; and

(b3) using the calculated set-points to control the positioning systemto apply the device pattern to the substrate.

The invention in a fourth aspect provides an apparatus for controlling apositioning system of a lithographic apparatus for applying a devicepattern at multiple locations across a substrate, the apparatuscomprising a data processing apparatus programmed to perform the stepsof:

-   -   receiving a height map of a substrate that has been subjected to        lithographic processing over a plurality of device areas;    -   subtracting from the height map a first height map component        representing topographical variations associated with the device        pattern so as to obtain one or more further height map        components representing other topographical variations;    -   using the obtained height map component(s), calculating control        set-points according to a control algorithm specific to the        other topographical variations; and    -   combining the control set-points calculated for the first height        map component and the further height map component(s) and    -   providing set-points to control the positioning system to apply        the device pattern to the substrate.

The third and fourth aspects of the invention are therefore specialcases of the first and second aspects, which may be used whendevice-specific topography is to be ignored. The applicant reserves theright to claim these aspects independently.

The invention yet further provides a lithographic apparatus comprising aprojection system and positioning system for positioning a patterningdevice and substrate in relation to the projection system for applying apattern to a substrate, the lithographic apparatus including apparatusfor controlling the positioning system in accordance with the firstand/or second aspect of the invention as set forth above.

The invention yet further provides a computer program product comprisingmachine readable instructions for causing a general purpose dataprocessing apparatus to perform the steps of the method of the firstaspect of the invention as set forth above.

The invention yet further provides a computer program product comprisingmachine readable instructions for causing a general purpose dataprocessing apparatus to implement the apparatus of the second aspect ofthe invention as set forth above.

The computer program product in either case may comprises anon-transitory storage medium.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings. It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in which:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 shows schematically the use of the lithographic apparatus of FIG.1 together with other apparatuses forming a production facility forsemiconductor devices;

FIG. 3 illustrates schematically the operation of a height sensor andvarious phenomena of localized topographical variations on an examplesubstrate in the lithographic apparatus of FIG. 1;

FIG. 4 is a schematic diagram of a focus control operation when applyinga pattern to the substrate of FIG. 3, with the addition ofdevice-specific topographic variations;

FIG. 5 illustrates steps of a method of controlling focus of thelithographic apparatus in accordance with embodiments of the presentinvention; and

FIG. 6 illustrates some variations of the method of FIG. 5 in accordancewith alternative embodiments of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 schematically depicts a lithographic apparatus LA. The apparatuscomprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or EUV radiation).

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask or reticle) MA and connected to a firstpositioner PM configured to accurately position the patterning device inaccordance with certain parameters;

a substrate table (e.g. a wafer table) WTa or WTb constructed to hold asubstrate (e.g. a resist coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structuremay ensure that the patterning device is at a desired position, forexample with respect to the projection system. Any use of the terms“reticle” or “mask” herein may be considered synonymous with the moregeneral term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device (or a number of devices) beingcreated in the target portion, such as an integrated circuit. Thepatterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g. water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system Immersion techniques are wellknown in the art for increasing the numerical aperture of projectionsystems. The term “immersion” as used herein does not mean that astructure, such as a substrate, must be submerged in liquid, but ratheronly means that liquid is located between the projection system and thesubstrate during exposure.

Illuminator IL receives a radiation beam from a radiation source SO. Thesource and the lithographic apparatus may be separate entities, forexample when the source is an excimer laser. In such cases, the sourceis not considered to form part of the lithographic apparatus and theradiation beam is passed from the source SO to the illuminator IL withthe aid of a beam delivery system BD comprising, for example, suitabledirecting mirrors and/or a beam expander. In other cases the source maybe an integral part of the lithographic apparatus, for example when thesource is a mercury lamp. The source SO and the illuminator IL, togetherwith the beam delivery system BD if required, may be referred to as aradiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as G-outer andG-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross section.

The radiation beam B is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam B passes through the projection system PS, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate tableWTa/WTb can be moved accurately, e.g. so as to position different targetportions C in the path of the radiation beam B. Similarly, the firstpositioner PM and another position sensor (which is not explicitlydepicted in FIG. 1) can be used to accurately position the mask MA withrespect to the path of the radiation beam B, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe mask table MT may be realized with the aid of a long-stroke module(coarse positioning) and a short-stroke module (fine positioning), whichform part of the first positioner PM. Similarly, movement of thesubstrate table WTa/WTb may be realized using a long-stroke module and ashort-stroke module, which form part of the second positioner PW. In thecase of a stepper (as opposed to a scanner) the mask table MT may beconnected to a short-stroke actuator only, or may be fixed. Mask MA andsubstrate W may be aligned using mask alignment marks M1, M2 andsubstrate alignment marks P1, P2. Although the substrate alignment marksas illustrated occupy dedicated target portions, they may be located inspaces between target portions (fields), and/or between device areas(dies) within target portions. These are known as scribe-lane alignmentmarks, because individual product dies will eventually be cut from oneanother by scribing along these lines. Similarly, in situations in whichmore than one die is provided on the mask MA, the mask alignment marksmay be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WTa/WTb arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WTa/WTb is then shifted inthe X and/or Y direction so that a different target portion C can beexposed. In step mode, the maximum size of the exposure field limits thesize of the target portion C imaged in a single static exposure.2. In scan mode, the mask table MT and the substrate table WTa/WTb arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WTa/WTb relative to themask table MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate tableWTa/WTb is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWTa/WTb or in between successive radiation pulses during a scan. Thismode of operation can be readily applied to maskless lithography thatutilizes programmable patterning device, such as a programmable mirrorarray of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Lithographic apparatus LA in this example is of a so-called dual stagetype which has two substrate tables WTa and WTb and two stations—anexposure station and a measurement station—between which the substratetables can be exchanged. While one substrate on one substrate table isbeing exposed at the exposure station EXP, another substrate can beloaded onto the other substrate table at the measurement station MEA sothat various preparatory steps may be carried out. The preparatory stepsmay include mapping the surface height of the substrate using a heightsensor LS and measuring the position of alignment marks on the substrateusing an alignment sensor AS. The measurement is time-consuming and theprovision of two substrate tables enables a substantial increase in thethroughput of the apparatus. If the position sensor IF is not capable ofmeasuring the position of the substrate table while it is at themeasurement station as well as at the exposure station, a secondposition sensor may be provided to enable the positions of the substratetable to be tracked at both stations.

The apparatus further includes a lithographic apparatus control unitLACU which controls all the movements and measurements of the variousactuators and sensors described. LACU also includes signal processingand data processing capacity to implement desired calculations relevantto the operation of the apparatus. In practice, control unit LACU willbe realized as a system of many sub-units, each handling the real-timedata acquisition, processing and control of a subsystem or componentwithin the apparatus. For example, one processing subsystem may bededicated to servo control of the substrate positioner PW. Separateunits may even handle coarse and fine actuators, or different axes.Another unit might be dedicated to the readout of the position sensorIF. Overall control of the apparatus may be controlled by a centralprocessing unit, communicating with these sub-systems processing units,with operators and with other apparatuses involved in the lithographicmanufacturing process.

FIG. 2 at 200 shows the lithographic apparatus LA in the context of anindustrial production facility for semiconductor products. Within thelithographic apparatus (or “litho tool” 200 for short), the measurementstation MEA is shown at 202 and the exposure station EXP is shown at204. The control unit LACU is shown at 206. Within the productionfacility, apparatus 200 forms part of a “litho cell” or “litho cluster”that contains also a coating apparatus 208 for applying photosensitiveresist and other coatings to substrate W for patterning by the apparatus200. At the output side of apparatus 200, a baking apparatus 210 anddeveloping apparatus 212 are provided for developing the exposed patterninto a physical resist pattern.

Once the pattern has been applied and developed, patterned substrates220 are transferred to other processing apparatuses such as areillustrated at 222, 224, 226. A wide range of processing steps isimplemented by various apparatuses in a typical manufacturing facility.For the sake of example, apparatus 222 in this embodiment is an etchingstation, and apparatus 224 performs a post-etch annealing step. Furtherphysical and/or chemical processing steps are applied in furtherapparatuses, 226, etc. Numerous types of operation can be required tomake a real device, such as deposition of material, modification ofsurface material characteristics (oxidation, doping, ion implantationetc.), chemical-mechanical polishing (CMP), and so forth. The apparatus226 may, in practice, represent a series of different processing stepsperformed in one or more apparatuses.

As is well known, the manufacture of semiconductor devices involves manyrepetitions of such processing, to build up device structures withappropriate materials and patterns, layer-by-layer on the substrate.Accordingly, substrates 230 arriving at the litho cluster may be newlyprepared substrates, or they may be substrates that have been processedpreviously in this cluster or in another apparatus entirely. Similarly,depending on the required processing, substrates 232 on leavingapparatus 226 may be returned for a subsequent patterning operation inthe same litho cluster, they may be destined for patterning operationsin a different cluster, or they may be finished products to be sent fordicing and packaging.

Each layer of the product structure requires a different set of processsteps, and the apparatuses 226 used at each layer may be completelydifferent in type. Moreover, different layers require different etchprocesses, for example chemical etches, plasma etches, according to thedetails of the material to be etched, and special requirements such as,for example, anisotropic etching.

The previous and/or subsequent processes may be performed in otherlithography apparatuses, as just mentioned, and may even be performed indifferent types of lithography apparatus. For example, some layers inthe device manufacturing process which are very demanding in parameterssuch as resolution and overlay may be performed in a more advancedlithography tool than other layers that are less demanding. Thereforesome layers may be exposed in an immersion type lithography tool, whileothers are exposed in a ‘dry’ tool. Some layers may be exposed in a toolworking at DUV wavelengths, while others are exposed using EUVwavelength radiation.

The whole facility may be operated under control of a supervisorycontrol system 238, which receives metrology data, design data, processrecipes and the like. Supervisory control system 238 issues commands toeach of the apparatuses to implement the manufacturing process on one ormore batches of substrates.

Also shown in FIG. 2 is a metrology apparatus 240 which is provided formaking measurements of parameters of the products at desired stages inthe manufacturing process. A common example of a metrology apparatus ina modern lithographic production facility is a scatterometer, forexample an angle-resolved scatterometer or a spectroscopicscatterometer, and it may be applied to measure properties of thedeveloped substrates at 220 prior to etching in the apparatus 222. Usingmetrology apparatus 240, it may be determined, for example, thatimportant performance parameters such as overlay or critical dimension(CD) do not meet specified accuracy requirements in the developedresist. Prior to the etching step, the opportunity exists to strip thedeveloped resist and reprocess the substrates 220 through the lithocluster. As is also well known, the metrology results 242 from theapparatus 240 can be used to maintain accurate performance of thepatterning operations in the litho cluster, by control unit LACU 206making small adjustments over time, thereby minimizing the risk ofproducts being made out-of-specification, and requiring re-work. Ofcourse, metrology apparatus 240 and/or other metrology apparatuses (notshown) can be applied to measure properties of the processed substrates232, 234, and incoming substrates 230.

Referring now to FIG. 3, it was mentioned above that a preliminary stepin the operation of a lithographic apparatus is for a map of substrateheight to be obtained by measuring surface position in the Z directionagainst X-Y position. This height map may be obtained for example usingthe height sensor LS in the lithographic apparatus of FIG. 1, after thesubstrate has been clamped to one of the substrate supports WTa and WTb.The height map is used during patterning to achieve accurate focusing ofan image of the patterning device MA onto the substrate. A substratesupport is labeled WT, and carries a substrate W. The height sensor LSis in this example an optical sensor, comprising a source side opticsLSS, and detector optics LSD. Other types of height sensors includingfor example air gauge sensors are known, which may be used instead of orin combination with the optical sensor. (For example, an air gaugesensor may be used as a process-independent measurement by whichmeasurements from the optical sensor LS can be calibrated).Alternatively metrology tools outside the lithographic apparatus may beused to determine a topography within the die. Even furtheralternatively, (different layers of) design data may be used (alone orin combination with already indicated techniques) to estimate the devicetopography. In such an embodiment, the estimation of the topography maybe done on data alone, without direct measurements on the substrate W.

In operation, source side optics LSS generates one or more beams ofradiation (light) 310 that impinge onto a substrate W. Substrate Wtypically has different layers formed on it, and typically many morelayers than are illustrated here. A top layer will normally be theresist layer 312 in which a pattern is to be formed. Below that will bean anti-reflective coating and below that will be potentially manylayers of device features formed in different layouts and materials.

The beam of light 310 is reflected by the substrate and detected bydetector side optics LSD to obtain one or more signals S(x,y) from whicha measurement of the surface height at a position (x,y) on the substratecan be derived. By measuring height at numerous positions across thesubstrate, a height map h(x,y) can be obtained by a suitable processorin control unit LACU. The height map is then used when the substrate isin the exposure station EXP, to control focus and other parameters inthe operation of the lithographic apparatus. The details of these opticsfor height sensing, as well as the associated signal processing, areknown in the art and described for example in the prior publicationsmentioned in the introduction. They will not be described herein indetail. The radiation used in the present examples may be monochromatic,polychromatic and/or broadband. It may be P- or S-polarized, circularlypolarized and/or unpolarized.

The sensor signals and/or the resulting height map may be subject tovarious corrections before being used to control focusing. As mentioned,for example, calibrations may be applied based on process-independentmeasurements made using an air gauge or the like. Corrections to reduceprocess dependency can also be applied based on knowledge of the productdesign and processing. This is described further in patent applicationEP14157664.5, mentioned above.

The height map h(x,y) can take any suitable form. In a simpleembodiment, the height map comprises a two-dimensional array of samplevalues indexed by the X and Y coordinates of position across thesubstrate. In other embodiments, the height values could be expressed byparametric curves, fitted to measured sample values. A graph 314 ofh(x,y) in FIG. 3 represents height values in a single slice, for exampleextending in the Y direction with a certain X value.

Over most of the substrate surface, height variations are conventionallyrelatively gentle, both in extent and their degree of localization(spatial frequency). In the enlarged detail at the bottom of FIG. 3,however, some different types of height anomalies are illustrated thatcan be found as localized topographical variations in a real process.For example, a steeper variation may arise in a region 316 towards theedge 318 of the substrate, in a peripheral region of the substrate. Thevariation near the substrate edge can have many causes. Non-uniformityleading to edge effects may arise in the manufacture of the originalsubstrate W, and even in the manufacture of the substrate support WTitself. Subsequently, variations in etching, CMP and the like mayaccumulate layer-by-layer so that a phenomenon known as “edge roll-off”becomes quite pronounced. Although the term “roll-off” naturally impliesa downward slope in surface height towards the edge, as illustrated inFIG. 3, an upward slope could occur, with the same results. Furthermore,although the phenomenon of edge roll-off will be referred to in thepresent disclosure as an example, the disclosure applies equally to anynon-device specific topography related to the edge region of thesubstrate. For example there may be height steps in exposed fields thatneighbor non-exposed edge fields.

In another region 320, a dip or hole 322 can be seen in the surface.This can have a number of causes. In a particular example, the hole mayarise at a location where there is a gap in the pattern of projectionsknown as burls 322, that typically support the back side of thesubstrate. A gap in the burl pattern may be necessary for example toallow an ejector pin, an air duct or some other actuator or sensor to bepresent on the surface of the substrate support. Of course, suchfeatures have been present in substrate tables in the past. However,performance requirements become ever tighter, and anomalies that couldbe ignored in previous generations of products gradually becomesignificant limitations of the performance and/or yield of thelithographic apparatus as a whole.

Moreover, some modern types of product such as 3-D memory circuits maybe particularly susceptible to formation of a hole 322. This is becausethe formation of dense 3-D structures on the substrate can impart stresspatterns not present in more conventional products. Therefore thesubstrate is less inclined to remain flat in the absence of back sidesupport. It is also mentioned that a gap in the pattern of burls doesnot necessarily lead to a dip in the wafer surface. The shape is definedby a balance of forces at each location, for example clamping forcesversus wafer stress. This might on occasion lead to a bump or, even aheight variation of a bump and a dip on a length scale smaller than thearea of missing burls.

In another region 330, a bump feature 332 is seen in the surface. Thisalso can have a number of causes. A common cause of bump features iscontamination, shown here for example by a contaminant particle 334trapped between the substrate W and substrate support WT. It is knownthat the short-range and large amplitude of these types of heightanomalies undesirably impacts the focusing of the image, and yield ofworking products can be impacted negatively as a result. Focus controlalgorithms can be optimized, either across the substrate or locally inknown “trouble spots”, to try and achieve successful focusing, and hencesuccessful imaging, even in these areas.

FIG. 4 illustrates focus control being performed on a substrate havingheight anomalies of the type described in FIG. 3, after substratesupport WT with substrate W has been transferred to the exposure stationEXP of the lithographic apparatus of FIG. 1. A focus control system 400comprises a focus controller 402 (which may be implemented for exampleas a numerical process within lithographic apparatus control unit LACU)and the apparatus hardware 404. Hardware 404 in this example includesthe various components of the positioners PM, PW and the projectionsystem PS shown in FIG. 1. These components have associated sensors andactuators communicating with controller 402.

Using the height map data h(x,y), controller 402 causes the projectionsystem controls the relative positions of the substrate W, theprojection system PS and the patterning device MA by a number of servoloops, so that an aerial image 406 of part of a field pattern isaccurately focused in the resist layer 312 on substrate W. It will beunderstood that the one-dimensional cross-section of FIG. 4 issimplified. Assuming a conventional scanning mode of operation, aerialimage 406 takes the form of a slit of radiation that extends in both Xand Y directions, while forming the focused image in a plane illustratedin cross-section in FIG. 4. In a scanning mode of operation, typicallythe extent of the imaging slit will be much wider in the slit direction(X) than it is in the scanning direction (Y).

Within certain performance limits, the height of the aerial image 406can be controlled continuously while the slit scans in the Y direction,to follow a desired set-point profile z(x,y). Similarly, rotations ofthe image plane around the X and Y axes can also be adjusted continuallyto follow respective set-point profiles (Rx(x,y) and Ry(x,y)). Assumingconventional arrangement, the x coordinate will not change during eachscan, but the x coordinate will change when the apparatus steps to eachnext field position. Other degrees of control may be provided: the onesmentioned are those relevant to focusing. Typically the extent of theimaging slit will be much wider in the slit direction (X) than it is inthe scanning direction (Y).

The set-point profiles Rx(x,y), Ry(x,y), z(x,y) are determined bycontroller 402 using the height map h(x,y) and an appropriate focuscontrol algorithm FOC. Broadly speaking focus errors inevitably ariseacross the area of the aerial image 406, because the focal plane is flatand the substrate surface is not flat. The algorithm operates byquantifying the focus error across the slit and adjusting the positionand orientation of the image plane until the focus error meets desiredcriteria. These criteria may include minimizing an average error (forexample minimizing a mean square error), and/or staying within a maximumfocus error over all or part of the image.

Additional criteria (constraints) may be defined by the dynamiccapabilities of the servo control mechanisms. The algorithm may need tosacrifice some focus performance in order not to violate theseconstraints. The controller may implement a “fall-back” algorithm as oneway to do this. In a known fall-back algorithm, if the preferredalgorithm yields a set-point profile that violates one of theconstraints, then the algorithm is adjusted to average focus errors overa larger slit size (without changing the actual slit size). This willhave the effect of averaging topographical variations over a wider area,and so the dynamics of the focal plane will tend to reduce. Thefall-back algorithm can be iterative if desired. In an extreme case, thealgorithm may decide to average focus errors over the whole field as asingle plane. As far as focus control is concerned, this extreme casecorresponds in effect to choosing the “stepping” mode of operationmentioned above. No variation of the focal plane is attempted across thewhole field.

Referring still to FIG. 4, the substrate in this illustration stillshows the edge, hole and bump anomalies in regions 316, 320 and 330.However, the substrate in this example also exhibits a strongdevice-specific topography. This is represented by high portions 440 andlow portions 442 that appear in a regular pattern defined by the devicelayout and processing effects arising in the formation of functionalstructures.

As illustrated, both the height amplitude and transverse distance scaleof the device-specific features may be comparable to those of theanomalies in regions 316, 320, 330. Consequently, if the focus controlalgorithm implemented in focus controller 402 is optimized to followclosely the short range variations due to edge effects, holes and bumps,there is a strong chance also that it will follow, or try to follow, thedevice specific topography. This is generally undesirable for goodimaging, as well as for dynamics of the many positioners and componentsthat are involved in imaging. Conversely, if the focus control algorithmimplemented in controller 402 is optimized to ignore the short-rangevariations that are characteristic of the device-specific topography,then its ability to maintain focus in the anomalous regions 316, 320 and330 will be limited, and yield in those areas will be reduced.

FIG. 5 is a data flow diagram of a modified focus control algorithm thatis implemented in the controller 402 of the lithographic apparatus ofFIG. 1 according to the present disclosure. This modified algorithmallows focus performance to be optimized under a wider range ofconditions than the known algorithms mentioned above. Processing beginsat 500 with receipt of the height map h(x,y) for a particular substrate.The height map represents a mixture of long-range and short-rangetopographic variations, which may include unknown height anomalies anddevice-specific topography. A first step 502 extracts a device-specificfeatures map h′(x,y) which represents a component of the topography thatrepeats between fields. A simple way to do this is to compare thetopography of each field with a smoothed copy of the height map, and totake the average of the comparison result over a representative sampleof the fields. In other words, an average field topography is obtainedas a way of obtaining the first height map component that representstopographical variations specific to the device pattern. The devicespecific topography can be regarded as a kind of intra-field fingerprintand may originate from any of the previously mentioned measurementand/or data sources.

While the device-specific topography can be obtained for a currentsubstrate by calculating an average field topography entirely from theheight map of the current substrate, the disclosure is not limited tosuch a case. The average field topography can be calculated frommeasurements of multiple substrates of the same product design andprocessing. The device-specific topography can be obtained wholly orpartly with regard to design information and knowledge of thetopographical effects of different processes. As mentioned, other typesof height sensor can also be brought into use. At the same time, thedesigner of the apparatus would need to confirm that using theseexternal or historic data improves accuracy and/or reduces processingrequirements, compared with simply using the height map of the currentsubstrate, as measured in the lithographic apparatus. These variationswill be illustrated further below, with reference to FIG. 6. In anycase, the device-specific topography is obtained at step 504.

On a real substrate, the amplitude of the device specific topography mayvary slightly over the substrate area. It is a matter of design choicewhether the device-specific topography is assumed, as an approximation,to be constant over the whole substrate, or whether, as an alternative,the variation in amplitude is captured and used. In the former case, thedevice-specific features map h′(x,y) may be reduced to the dimension ofa single field, if desired. Also, in the latter case, thedevice-specific features map could be reduced to a single fieldmultiplied by a scaling factor that varies with position over thesubstrate. Although in some cases the variation in amplitude may besmall over most of the substrate area, device-specific topography maybecome accentuated in the peripheral fields. Therefore modeling thisvariation of fingerprint amplitude can be particularly beneficial incases where edge-related topography and device-specific topography arefound together.

At 506 the topography represented in device-specific features maph′(x,y) is subtracted from the measured height map h(x,y) to extractwhat we may call a “global features” map h″(x,y). This global featuresmap represents a component of topography not associated with thespecific device pattern. This component may include the normallong-range height variations, but also any short-range height anomalies(such as bumps, holes, and edge effects) that do not repeat in the sameway as the device pattern. In a case where the imaging is performed onthe basis of a field pattern that includes a plurality of individualdevice patterns, it is a matter of design choice whether thedevice-specific features are identified on the scale of a single deviceor single field. For the present example, it is assumed thatdevice-specific features are identified on the scale of a field.

Having decomposed the original height map h(x,y) into separatecomponents h′(x,y) and h″(x,y), each component of the height map is thenprocessed by an algorithm specific to that component. Thus in theexample of FIG. 5, the focus controller continues at 508 by processingthe device-specific features map h′(x,y) using a first focus controlalgorithm FOC′. The first focus control algorithm FOC′ produces a firstset of set-point profiles Rx′(x,y), Ry′(x,y), z′(x,y). The controllerthen at 510 processes the global features map h″(x,y) using a secondfocus control algorithm FOC″. The second focus control algorithm FOC″produces a second set of set-point profiles Rx″(x,y), Ry″(x,y), z″(x,y).

At 512 the set-point profiles are added together to obtain a combinedset of set-point profiles Rx(x,y), Ry(x,y), z(x,y). The algorithms FOC′and FOC″ are thus summed into an overall focus control algorithm FOCthat is implemented by controller 402.

By splitting the device-specific features and the global features intoseparate components of the height map, for separate processing, thedisclosed apparatus allows optimized processing to be implemented foreach set of features separately. The first focus control algorithm FOC′produces a first set of set-point profiles Rx′(x,y), Ry′(x,y), z′(x,y)that are optimized for imaging with regard to the device specifictopography. The second focus control algorithm FOC″ produces a secondset of set-point profiles Rx″(x,y), Ry″(x,y), z″(x,y) that are optimizedfor imaging with regard to the device specific topography. Of course, inthe end the focus control is a compromise, but, because the two sets ofset-point values are only summed linearly (of course including differentweights for each component), there is not the problem that features ofone type will be undesirably magnified or suppressed, when one seeks tosuppress or magnify features of another type. Moreover, selection ofappropriate algorithms becomes much simpler, and the need to optimizealgorithms differently for each layer may be reduced also. Additionally,fall-back criteria can be set differently in the different features. Inother words, performance in relation to one set of features need not becompromised, just because fall-back is necessary to address challengingtopography in the other set of features.

As examples, for the first focus control algorithm FOC′, the set-pointcalculation can be optimized to suppress short-range effects. Forexample, the algorithm FOC′ may be one that minimizes a mean squarefocus error over a slit area. If the topography is challenging, dynamicconstraints may trigger a fall-back algorithm to enlarge the slit for asmoother profile in one or more dimensions. The fall-back criteria canbe optimized for the device-specific topography, without compromisingthe response to bumps, holes and edge effects.

Similarly, the second focus control algorithm FOC″ can be optimized tofollow short-range topographical variations as far as possible, withoutcompromising the smoothing of device-specific features. It can beoptimized to be particularly sensitive to extreme height values withinthe slit area (or the nominal slit area), without being sensitive toextreme height values that are features of the device-specifictopography. For example, to enhance the response to short-rangeanomalies, algorithm FOC″ may be one that minimizes a quartic (fourthpower) of the focus errors, or even an eighth power. While suchalgorithms are known for applying increased weight to the extreme valuespresent in anomaly regions, they could not normally be deployed in thepresence of significant device-specific topography. Because thecombination of set-points at 512 is linear, the fourth power or eighthpower calculations can be employed in algorithm FOC″ without amplifyingthe device-specific topography. Again, fall-back criteria and fall-backresponses can be optimized for the global features separately from thedevice-specific features. In general, therefore, the method disclosedallows the separate calculations to have different degrees ofnonlinearity.

Numerous variations of the above examples can be envisaged within thescope of the present disclosure.

Although in the above example, the topographic variations have beendecomposed into just two components (h′ and h″), there may be cases alsowhere it is useful to decompose the variations into more than twocomponents and allow each of them to have a different focus controlalgorithm. As an example where this might be useful, one could choose toseparate hole and bump type features into a different component fromedge-related variations. The non-device specific component h″ could beseparated into two or more components. In another example, it might beuseful to provide different algorithms for handling edge-relatedvariations in different quadrants of the circumference. In particular,because of the different orientation of the edge relative to the slitused for imaging, different criteria should maybe applied toedge-related variations in these different areas. Also with regard tothe device-specific topography, one could further separate it into twoor more components. One could envisage in this regard identifying andprocessing separately variations in the X and Y directions.Alternatively or in addition, one could identify separately thevariations on a device area basis and a field basis. In any case, theskilled reader can readily extend the concept of the method illustratedin FIG. 5, to provide for three or more components.

Another variation is illustrated as step 516 in FIG. 5. It is oftendesired to generate extrapolated height data for points beyond the fieldboundary, particularly in the scanning (Y direction). This is to obtaina smooth control at the beginning and end of the scan of each field.Generally it is desirable for the extrapolation to take account of localheight variations (gradients) up to the field edge. Particularly in theperipheral fields, there may not even be height data for parts of thefield itself, that fall beyond the substrate edge. Extrapolation will beuseful in these cases also, to “fill in” the missing part of the field.However, in examples with strong device-specific topography, toextrapolate on the basis of variations that are actually justdevice-specific variations would cause a poor performance.

Consequently, in cases with significant device-specific topography, thebest option is frequently to base the extrapolation assuming a planarfield (similar to the fall-back behavior described above). In the methodof FIG. 5, however, the device-specific height variations h′ have beenseparated from the non-device specific component h″. The extrapolationstep 516 can therefore safely be performed using the component h″,without being influenced undesirably by presence of device-specificheight variations. In other words, the height map data used forextrapolation excludes the device-specific component of the height mapdata, and the extrapolated height values are insensitive totopographical variations associated with the device pattern.

In the above example, a simple linear combination of the first andsecond sets of control set-points is proposed. The focus controlset-points calculated in steps 508 and 510 may both be expressedrelative to a common reference height and averaged in step 512.Alternatively, the focus control set-points calculated in step 508 maybe expressed as deviations from zero, simply added in step 512 to theset-points calculated in step 510.

The combination may apply equal weights to both components, or it mayapply unequal weights, according to experience or design. The weightingmay also be made automatically responsive to conditions encountered inthe measured data or other information used. In the case of averaging, aweighted average may be applied. In the case where one of the controlset-points is expressed as a deviation from the other, it may beweighted by applying a scaling factor greater than or less than 1.

In the extreme case where the weighting to be applied to (say) thedevice-specific set-points would be zero, it would not be necessary touse the device specific component to calculate control set-points atall. Step 508 would be omitted, or replaced by a constant set-pointoffset. For example, if a most critical region of the device pattern isknown to require focusing 20 nm above the general height indicated bythe height map, then the first control algorithm FOC′ may comprisesimply adding a constant height offset. More generally, the calculationat step 508 and/or 510 can be performed to apply enhanced weighting toheight values in critical regions defined by the user.

The combination of the two or more sets of control set-points need notbe linear. On the other hand the use of a nonlinear combination wouldbring a particular weighing or de-weighting to extreme set-point values.

Additionally, either or both of the calculations performed in step 508and 510 can be performed so as to apply enhanced weight to height valuesin regions of the product design that are identified by a user ascritical. Often the finest features, on which the performance of thewhole product may depend, are concentrated in a particular region of thedevice area. Reduced focus performance in other regions may be tolerablewithout degrading the performance of the finished product.

FIG. 6 illustrates some of the above variations graphically, withoutimplying that they must all be combined in the same embodiment. Stepslabeled 600 to 614 correspond to the like-numbered steps 500-514 in FIG.5 and will not be described again, except to highlight differences.

As a first variant, in FIG. 6 the device specific topography h′(x,y)obtained at step 604 is not derived, or not entirely derived, from theheight map obtained at step 600. At 620 some prior knowledge based ondesign information and/or measurements of prior substrates is used todefine the device specific topography.

As another variant, prior knowledge is obtained in a step 622 and usedto influence the calculation of the second first focus controlset-points in step 608. As another variant, prior knowledge is obtainedin a step 624 and used to influence the calculation of the first focuscontrol set-points in step 610.

As another variant, step 608 is performed to calculate first focuscontrol set-points without reference to the device-specific topography.

In conclusion, by decoupling the set-point calculation with regard tosystematic (intrafield) device features from the set-point calculationwith regard to global shape and process effects of the substrate,control of imaging parameters such as focus becomes more reliable andsimplified. Where previously focus optimization might require a delicatedesign decision for every individual layer of a product, the decouplingof the calculations increases the chance that a good performance will beobtained with the same algorithms at every layer. Further adjustmentscan be made in the separate calculations, to optimize performance ineach layer, without fear of unexpected side-effects.

The invention may further be described using the following clauses:

1. A method of controlling a lithographic apparatus to manufacture aplurality of devices on a substrate, the method comprising:

(a) obtaining a height map representing a topographical variation acrossthe substrate; and

(b) using the height map to control a positioning system of thelithographic apparatus for applying a device pattern at multiplelocations across the substrate

wherein step (b) comprises:

(b1) decomposing the height map into a plurality of components,including a first height map component representing topographicalvariations associated with the device pattern and one or more furtherheight map components representing other topographical variations;

(b2) using each height map component, calculating control set-pointsaccording to a control algorithm specific to each component; and

(b3) combining the control set-points calculated for the first heightmap component and the further height map component(s) and using thecombined set-points to control the positioning system to apply thedevice pattern to the substrate.

2. A method according to clause 1, wherein the step (b1) comprisescalculating the first component of the height map based on an averagefield topography and subtracting the first component from the height mapto obtain said further height map component.

3. A method according to clause 1 or 2, wherein in step (b2) analgorithm specific to the first height map component is less responsiveto short-range topographic variations than an algorithm specific to thefurther height map component.

4. A method according to clause 1, 2 or 3, wherein in step (b2) one ormore of the algorithms specific to the different height map componentshave nonlinearity, while the combining of the control set-points in step(b3) is performed linearly.

5. A method according to any preceding clause, wherein the lithographicapparatus is of a scanning type and wherein the algorithm specific tothe first height map component is permitted to consider values from adifferent sized portion of the field than an algorithm specific to afurther height map component.6. A method according to any preceding clause, wherein the step (b2)includes using the height map data to generate additional height mapdata by extrapolation, and wherein the height map data used forextrapolation excludes the first height map component so that theextrapolated height map data is insensitive to topographical variationsassociated with the device pattern.7. An apparatus for controlling a positioning system of a lithographicapparatus for applying a device pattern at multiple locations across asubstrate, the apparatus comprising a data processing apparatusprogrammed to perform the steps of:

-   -   receiving a height map of a substrate that has been subjected to        lithographic processing over a plurality of device areas;    -   decomposing the height map into a plurality of components,        including a first height map component representing        topographical variations associated with the device pattern and        one or more further height map components representing other        topographical variations;    -   using each height map component, calculating control set-points        according to a control algorithm specific to each component; and    -   combining the control set-points calculated for the first height        map component and the further height map component(s) and    -   providing set-points to control the positioning system to apply        the device pattern to the substrate.        8. An apparatus according to clause 7, wherein for decomposing        the height map the processor is arranged to calculate the first        component of the height map based on an average field topography        and to subtract the first component from the height map to        obtain said further height map component.        9. An apparatus according to clause 7 or 8, wherein an algorithm        specific to the first height map component is less responsive to        short-range topographic variations than an algorithm specific to        the further height map component.        10. An apparatus according to clause 7, 8 or 9, wherein one or        more of the algorithms specific to the different height map        components have nonlinearity, while the combining of the control        set-points is performed linearly.        11. An apparatus according to any of the clauses 7 to 10,        wherein the lithographic apparatus is of a scanning type and        wherein the algorithm specific to the first height map component        is permitted to consider values from a different sized portion        of the field than the algorithm specific to the further height        map component.        12. An apparatus according to any of the clauses 7 to 11,        wherein the calculating of control set-points for at least one        of the components includes using the height map data to generate        additional height map data by extrapolation, and wherein the        height map data used for extrapolation excludes the first height        map component, so that the extrapolated height map data is        insensitive to topographical variations associated with the        device pattern.        13. A method of controlling a lithographic apparatus to        manufacture a plurality of devices on a substrate, the method        comprising:

(a) obtaining a height map representing a topographical variation acrossthe substrate; and

(b) using the height map to control a positioning system of thelithographic apparatus for applying a device pattern at multiplelocations across the substrate

wherein step (b) comprises:

(b1) subtracting from the height map a first height map componentrepresenting topographical variations associated with the device patternso as to obtain one or more further height map components representingother topographical variations;

(b2) using the obtained height map component(s), calculating controlset-points according to a control algorithm specific to the othertopographical variations; and

(b3) using the calculated set-points to control the positioning systemto apply the device pattern to the substrate.

14. An apparatus for controlling a positioning system of a lithographicapparatus for applying a device pattern at multiple locations across asubstrate, the apparatus comprising a data processing apparatusprogrammed to perform the steps of:

-   -   receiving a height map of a substrate that has been subjected to        lithographic processing over a plurality of device areas;    -   subtracting from the height map a first height map component        representing topographical variations associated with the device        pattern so as to obtain one or more further height map        components representing other topographical variations;    -   using the obtained height map component(s), calculating control        set-points according to a control algorithm specific to the        other topographical variations; and    -   combining the control set-points calculated for the first height        map component and the further height map component(s) and    -   providing set-points to control the positioning system to apply        the device pattern to the substrate.        15. A lithographic apparatus comprising a projection system and        positioning system for positioning a patterning device and        substrate in relation to the projection system for applying a        pattern to a substrate, the lithographic apparatus being        arranged to control the positioning system by a method according        to any of the clauses 1 to 6 and 13.        16. A lithographic apparatus comprising a projection system and        positioning system for positioning a patterning device and        substrate in relation to the projection system for applying a        pattern to a substrate, the lithographic apparatus including        apparatus according to any of the clauses 7 to 12 and 14 for        controlling the positioning system.        17. A computer program product comprising machine readable        instructions for causing a general purpose data processing        apparatus to perform the steps of a method according to any of        the clauses 1 to 6 and 13.        18. A computer program product comprising machine readable        instructions for causing a general purpose data processing        apparatus to implement the apparatus according to any of the        clauses 7 to 12 and 14.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin film magneticheads, etc.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g. having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thespirit and scope of the claims set out below. In addition, it should beappreciated that structural features or method steps shown or describedin any one embodiment herein can be used in other embodiments as well.

The invention claimed is:
 1. A method comprising: obtaining a height maprepresenting a topographical variation across a substrate; and using theheight map to control a positioning system of a lithographic apparatusfor applying a product pattern at multiple locations across thesubstrate, wherein using the height map comprises: decomposing theheight map into a plurality of components, including a first height mapcomponent representing topographical variations associated with a devicepattern and a second height map component representing othertopographical variations; using each of the first and second height mapcomponents, calculating control set-points according to a controlalgorithm specific to each of the first and second height mapcomponents; combining the control set-points calculated for the firstheight map component and the second height map component; and using thecombined set-points to control the positioning system to apply theproduct pattern to the substrate.
 2. The method as claimed in claim 1,wherein the decomposing the height map comprises calculating the firstcomponent of the height map based on an average field topography andsubtracting the first component from the height map to obtain the secondheight map component.
 3. The method as claimed in claim 1, wherein inthe calculating control set-points an algorithm specific to the firstheight map component is less responsive to short-range topographicvariations than an algorithm specific to the second height mapcomponent.
 4. The method as claimed in claim 1, wherein in thecalculating control set-points one or more of the algorithms specific tothe different height map components have nonlinearity, while thecombining of the control set-points is performed linearly.
 5. The methodas claimed in claim 1, wherein the lithographic apparatus is of ascanning type and wherein the algorithm specific to the first height mapcomponent is permitted to consider values from a different sized portionof a field than an algorithm specific to the second height mapcomponent.
 6. The method as claimed in claim 1, wherein the calculatinga control set-point for at least one of the height map componentsincludes using the height map data to generate additional height mapdata by extrapolation, and wherein the height map data used forextrapolation excludes the first height map component so that theextrapolated height map data is insensitive to topographical variationsassociated with the device pattern.
 7. An apparatus comprising a dataprocessing apparatus programmed to at least: receive a height map of asubstrate that has been subjected to lithographic processing; decomposethe height map into a plurality of components, including a first heightmap component representing topographical variations associated with adevice pattern and a second height map component representing othertopographical variations; using each of the first and second height mapcomponents, calculate control set-points according to a controlalgorithm specific to each of the first and second height mapcomponents; combine the control set-points calculated for the firstheight map component and the second height map component; and provide aset-point, based on the combination of the control set-points, tocontrol a positioning system of a lithographic apparatus configured toapply a product pattern at multiple substrate locations.
 8. Theapparatus as claimed in claim 7, wherein, to decompose the height map,the data processing apparatus is arranged to calculate the firstcomponent of the height map based on an average field topography and tosubtract the first component from the height map to obtain the secondheight map component.
 9. The apparatus as claimed in claim 7, wherein analgorithm specific to the first height map component is less responsiveto short-range topographic variations than an algorithm specific to thesecond height map component.
 10. The apparatus as claimed in claim 7,wherein one or more of the algorithms specific to the different heightmap components have nonlinearity, while the combination of the controlset-points is performed linearly.
 11. The apparatus as claimed in claim7, wherein the lithographic apparatus is of a scanning type and whereinthe algorithm specific to the first height map component is permitted toconsider values from a different sized portion of a field than thealgorithm specific to the second height map component.
 12. The apparatusas claimed in claim 7, wherein the calculation of a control set-pointfor at least one of the height map components includes using the heightmap data to generate additional height map data by extrapolation, andwherein the height map data used for extrapolation excludes the firstheight map component, so that the extrapolated height map data isinsensitive to topographical variations associated with the devicepattern.
 13. A method comprising: obtaining a height map representing atopographical variation across a substrate; and using the height map tocontrol a positioning system of a lithographic apparatus for applying aproduct pattern at multiple locations across the substrate, whereinusing the height map comprises: subtracting from the height map a firstheight map component representing topographical variations associatedwith a device pattern so as to obtain a second height map componentrepresenting other topographical variations; using the obtained secondheight map component, calculating control set-points according to acontrol algorithm specific to the other topographical variations; andusing the calculated set-points to control the positioning system toapply the product pattern to the substrate.
 14. An apparatus comprisinga data processing apparatus programmed to at least: receive a height mapof a substrate that has been subjected to lithographic processing;subtract from the height map a first height map component representingtopographical variations associated with a device pattern so as toobtain a second height map component representing other topographicalvariations; using the obtained second height map component, calculatecontrol set-points according to a control algorithm specific to theother topographical variations; combine the control set-pointscalculated for the first height map component and the second height mapcomponent; and provide a set-point, based on the combination of thecontrol set-points, to control a positioning system of a lithographicapparatus configured to apply a product pattern at multiple substratelocations.
 15. A non-transitory computer program product comprisingmachine readable instructions therein that, when executed, areconfigured to cause a general purpose data processing apparatus to atleast: obtain a height map representing a topographical variation acrossa substrate; and use the height map to control a positioning system of alithographic apparatus for applying a product pattern at multiplelocations across the substrate, wherein use of the height map comprises:(a) decomposition of the height map into a plurality of components,including a first height map component representing topographicalvariations associated with a device pattern and a second height mapcomponent representing other topographical variations, calculation ofcontrol set-points according to a control algorithm specific to each ofthe first and second height map components, combination of the controlset-points calculated for the first height map component and the secondheight map component, and use of the combined set-points to control thepositioning system to apply the product pattern to the substrate, or (b)subtraction from the height map a first height map componentrepresenting topographical variations associated with a device patternso as to obtain a second height map component representing othertopographical variations, calculation of control set-points, using theobtained second height map component, according to a control algorithmspecific to the other topographical variations, and use of thecalculated set-points to control the positioning system to apply theproduct pattern to the substrate.
 16. The computer program product ofclaim 15, wherein use of the height map comprises: decomposition of theheight map into a plurality of components, including a first height mapcomponent representing topographical variations associated with thedevice pattern and a second height map component representing othertopographical variations, calculation of control set-points according toa control algorithm specific to each of the first and second height mapcomponents, combination of the control set-points calculated for thefirst height map component and the second height map component, and useof the combined set-points to control the positioning system to applythe product pattern to the substrate.
 17. The computer program productof claim 16, wherein the decomposition of the height map comprisescalculation of the first component of the height map based on an averagefield topography and subtraction of the first component from the heightmap to obtain the second height map component.
 18. The computer programproduct of claim 15, wherein use of the height map comprises:subtraction from the height map a first height map componentrepresenting topographical variations associated with the device patternso as to obtain a second height map component representing othertopographical variations, calculation of control set-points, using theobtained second height map component, according to a control algorithmspecific to the other topographical variations, and use of thecalculated set-points to control the positioning system to apply theproduct pattern to the substrate.
 19. A lithographic apparatuscomprising a projection system and a positioning system configured toposition a patterning device and substrate in relation to the projectionsystem in order to apply a pattern to a substrate, the lithographicapparatus comprising the apparatus of claim 7 to control the positioningsystem.
 20. A lithographic apparatus comprising a projection system anda positioning system configured to position a patterning device andsubstrate in relation to the projection system in order to apply apattern to a substrate, the lithographic apparatus comprising theapparatus of claim 14 to control the positioning system.